Known in the art is a method for making products from powdered heat-resistant materials by hot impact extrusion, comprising preparing cylindrical compacts by using conventional techniques of powder metallurgy, hydrostatic pressing of compacts under a pressure of 150 to 460 MN/m.sup.2, sintering them in vacuum at up to 1450.degree. C. during 1 to 6 hours, and subjecting the compacts to hot dynamic extrusion with glass lubricant, with subsequent annealing in vacuum during one hour (Abstr. Jr. "Metallurgia", 1981, 1.GAMMA.445; City of London Polytechnic, Dep. of Metallurgy and Materials. Ill. 12; Table ; ref. 9. "Hot Impact Extrusion and Subsequent Treatment of Some High-Temperature Nickel Alloys"). The dynamic extrusion allows high-temperature nickel-based alloys containing less than 50% of a high-melting component to be processed, and in certain applications it is capable of hot hardness, lowering porosity and distribution of particles in the material.
The main disadvantages of this method are due to its multiple-stage implementation which results in a substantial energy consumption, the need to use sophisticated production equipment, long process time and high labour effort. In addition, it is known that sophisticated alloys containing more than 50% of a high-melting component are not suitable for dynamic extrusion because of high hot and hardness.
Known in the art is a method for making products from hard alloy composite comprising carrying out a combustion reaction in a mixture of starting powders (metal, nonmetal and binder), with subsequent deformation of the mixture by three-dimensional compression ("New Methods for Making High-Temperature Materials Based on Combustion". Merzhanov A. G., Borovinskaya I. P., Yukhvid V. I., Ratnikov V. I. in the book "Scientific Fundamentals of Materials Technology" (in Russian). Moscow, Nauka Publishing House, 1981. pp. 193-206). This method can be regarded as a modification of hot pressing in which the combustion process prepares components for deformation of the material synthesis and heating). This method was used for making a tungsten-free hard alloy from elements (Ti, C, Ni, Mo). The mixture is blended for obtaining industrial alloys (titanium carbide with 20 and 30% of nickel and molybdenum binder). Materials with rather good properties close to commercially applicable grades can be produced under certain conditions. The method of self-propagating high-temperature synthesis under compression is used nowadays also for producing compact material from individual high-melting compounds.
The abovementioned method makes it possible to produce hard-alloy materials and products in a single stage during a short time period (about one munite) with minimum energy consumption.
The main disadvantage of the method is the limitation of configuration of products so that elongated products, i.e. products having a large length-to-diameter ratio (h/d&gt;&gt;1) are produced. The non-uniform three-dimensional compression pattern used in this method results in mainly compressive stresses being built up in the material. For this reason, if products with h/d&gt;1 are made by this method, they loose the initial shape with fracturing and underpressing.
Known in the art is a method of self-combustion sintering of ceramics under pressure, comprising propagation of exothermal synthesis reaction under a high pressure, wherein the synthesis and compaction of the sintered material are carried out in a blended powdery mixture containing elements necessary for the synthesis (Miyamoto K., Kamija H., Koizumi M. "High-Pressure Self-Combustion Sintering of Ceramics." Funtai oyobi Funmatsu Jaken. 1987, vol. 34. No. 3. pp. 101-196 (JP) CA 107 No 1. p. 266 (119811H). Abstr Jr. Khimia 1988, vol. 13, p. 11, 7E, 13M).
In this method, heat released as a result of the synthesis reaction is the source of energy for sintering under pressure. A thermal impulse should be applied to the mixture to initiate the process (by causing a current of 200-400A to flow during 3 seconds) whereafter the process occurs very rapidly (for about several seconds). High-melting materials such as TiB.sub.2, ZrB.sub.2, NbB.sub.2, TiC, SiC as well as composition materials and products on their base can be manufactured using this simultaneous synthesis and sintering.
Known in the art is an apparatus for carrying out this method comprising a reactor in which is placed into a high-pressure chamber. The reactor is in the form of a hexahedron of pyrophillite having boron nitride liners in which a starting mixture is charged. The mixture is ignited at one point or at the entire side surface thereof.
Advantages of the above described method and apparatus reside in a short process time and low power requirements. Disadvantage include equipment difficulties (an individual reactor is necessary for each size and shape of product), low productivity because the reactor should be placed in the high-pressure chamber, and product size limitation which is also imposed by the construction of the apparatus.
The most similar to the invention is a method for making products from powdered materials selected from the group consisting of at least one transition metal, at least one nonmetal, and at least one metal-based binder material, comprising preparing a powdery mixture of said materials, initiating a combustion reaction therein with the formation of a solid phase from said transition metal and nonmetal in the combustion products, with subsequent deformation of the combustion products and removal of the finished product.
Known in the art is an apparatus for carrying out this method, comprising a mold having a container for a powdery mixture, a device for initiating a combustion reaction in the mixture in the container, a punch for deforming the combustion products in the container, and a press for developing pressure for deforming the combustion products having a ram operatively connected to the punch and ram movement control system (Richardson G. Y., Rice R. W., McDonough W. J., Kunet J. M., Schroeter T. "Hot Pressing of Ceramics Using Self-Propagating Synthesis". Ceram. Eng. Sci. Proc. 1986, vol. 7, No. 7-8, pp. 761-770. Abstr. Jr. "Khimia., M., 1987, No. 4, 4II20).
In accordance with this method, the starting mixture is briquetted and placed into the apparatus.
The apparatus for carrying out the method comprises a graphite mold with a punch and a container lined with a layer of a fibrous ceramic insulation 1.5 cm thick. This facility makes it possible to carry out the induction heating of the mold to a high temperature (1000.degree. C.). Before initiation of the combustion reaction, a pressure of 34 MPa is applied to the briquet in the mold. The device for initiating the combustion reaction in the mixture is located outside the mold container, and a combustion wave propagates through the powdery mixture contained in a passage of the mold base, up to the briquet. After the ignition of the reagents the pressure materially drops (to about 50% of the initial value), and the pressure is then again raised to 34 MPa during about two seconds and is kept at this level during 5 to 10 minutes. The material is compacted by a hot forming press having a control system.
This method was used to make TiC-based materials containing 10-30 vol. % of Ti as binder and also TiC-TiB.sub.2 -based materials.
The above-described method and apparatus cannot be used for making elongated products (with a height-to-diameter ratio much greater than unity) because of the axial pressing resulting in compressive stresses only being built up in the material. Samples produced in the above described apparatus are in the form of discs 2.8 cm in diameter and 0.3 cm thick. Attempts to obtain products with h/d&gt;&gt;1 with such a loading pattern ended in fracturing of the sample and underpressing of certain portions.
In addition, there is no control of temperature of the material, which may result in non-uniformity of structure and composition of the material over the volume of the product. This inhomogeneity generally occurs in deforming materials in which components are in different states, e.g. the hard base is in the solid state and the metal binder is in the liquid state.